The embodiments described herein pertain generally to a apparatus and a method for mitigating or removing interference occurring between a macro-cell and a femto-cell.
In order to improve a capacity of a radio communication system, it is the most efficient to locate a transmitting end and a receiving end to be close to each other, and especially, a femto-cell technology is very efficient and effective in costs.
Since the femto-cell technology has potential advantages in view of improvement of an indoor area scope, energy efficiency and costs, it has been applied to a high-speed radio communication system. In addition, the femto-cell has been adopted as one of main functions of the LTE system, and an LTE femto-cell is advantageous in that it can use all bands defined in 3GPP and does not require a dedicated frequency band. For this reason, however, fatal co-channel interference between the macro-cell and the femto-cell may be caused.
Specifically, in a two-layer network, substantive interference problems may occur for the reason of scalability, security and limited availability of a backhaul bandwidth. In other words, using a macro-cell base station and a femto-cell base station on an identical spectrum is far more effective in view of social communication infrastructures or availability of a spectrum, but in this case, there is a problem because the two layers share a channel so that serious interference may occur in the shared channel. In recent, there have been suggested many methods to resolve the problem of interference that may occur in the network allowing co-existence of a femto-cell and a macro-cell.
Meanwhile, the primary demand for the macro-cell is related to enabling a user to conduct communication anytime, anywhere, and even during movement without a separate device, and many users receive a communication service from each macro-cell base station. Accordingly, it is desirable to preferentially secure a communication capacity of the macro-cell, compared to the femto-cell. That is, even if inter-layer interference exists with respect to the femto-cell, a minimum target SINR of a macro-cell user should be met.
To this end, it needs to be identified how much power in the femto-cell should be reduced to enable the macro-cell user to meet the target SINR, and an interference mitigation/removal method, which spends less time during processing of an interference mitigation/removal algorithm and has simple complexity to minimize latency as much as possible, is necessary. In addition, upon implementation of interference mitigation/removal, the process should be able to be combined with other resource managements like power and sub-channel assignment.
Accordingly, for mitigation/removal of interference in the two-layer network, the femto-cell should be able to conduct various measurements to offer sufficient information to the femto-cell, and simultaneously, maintain the coverage of the femto-cell.
For example, current LTE technology reports suggest various options for methods for information exchange between the macro-cell and the femto-cell. The methods include a method for information exchange between the macro-cell and the femto-cell through direct broadcasting between base stations, an information exchange method using broadcasting between a macro-cell base station and a femto-cell base station through a user device, a method for information exchange between a macro-cell base station and a femto-cell base station through X2-based interface as signaling protocol between base stations, a method for information exchange between a macro-cell base station and a femto-cell base station through S1-based interface as signaling protocol between a base station and a gateway, and others.
In this regard, Korean Patent Application No. 10-2009-0127908 (Method and Apparatus for Control of Interference of Base Station) suggests a method and an apparatus for controlling interference of a femto-cell base station, by converting an X2 interference control message used in an X2 interface into a format according to a protocol of an S1 interface to control interference occurring in a femto-cell environment having no X2 interface, so as to use a conventionally used X2 interference control message without newly defining an interface control message in the S1 interface.